Protective system



Feb. as, 1928. 1,660,965

w. HARTZELL PROTECTIVE SYSTEM Filed Aug. 25, 1922 H3. Fig, 2

I) l 2) z 3 WITNESSES- INVENTOR 5M 4 MM Wa/fer Harfzefl BY W R. (312ATTORNEY Patented Feb. 28, 1928.

PATENT OFFICE.

WALTER L. HARTZELL, OF CHICAGO, ILLINOIS.

PROTECTIVE SYSTEM.

Application filed August 25, 1922.

My invention relates toprotective systems and it has particular relationto the prevention oi abnormal opera ion of polyphase induction motorsand the lilre.

One object of my invention is to provide a relatively simple andinexpensive arrangement for preventing the single-phase operation of apolyphase induction motor.

Another object'ot my invention is to provide a polyphase motor circuitor the like with a protective device embodying means for inductivelyinterrupting one phase of the system upon an interruption of anotherphase.

Other and more specific objects of my invention will become evident fromthe following descri tion taltcn in conjunction with the accompanyingdrawing wherein,

Figure l is a diagrammatic view of a polyphase motor system equippedwith a protective device constructed and arranged in accordance with mypresent invention, and

Figure 2 is a similar view of a modification of the invention.

A large percentage of the burn-outs and similar failures of polyphaseinduction motors, for example, are due to the inadvertent single-phaseoperation thereoi whenever a single fuse or circuit-breaker in one phaseof the system opens that particular phase only. This condition mayobtain either when the motor is irst connected for the ap plication offull supply-circuit voltage, or by reason of the occurrence of abnormalloads during the running period thereof.

Mypresent invention is adapted to obviate the above-noted difficultiesby means of a" simple and inexpensive apparatus which may bevery readilyinstalled and, in fact, may be easily applied" to existinginstallations;

Referring to Figure 1 otthe drawing, the

system here showncomprises a'polyphase supply circuit includingconductors 1, 2 and 3 for supplying energy to a branch or customerscircuit including conductors 4, 5 and t5 that'are connected toapolyphase induction motor 7, for example. My protective device 8' isinterposed between the supply circuit and the induction motor to beprotected for preventing the single-phase operation thereof.

The protective device 8 comprises two circuit-interrupting means, suchas fuses 10 and 11, or the equivalent, that are respectively connectedin the branch conductors 4:

Serial No. 584,179.

and 5. These fuses arc of normal rating, corresponding to the motor 7while the third branch conductor or phase 6 may or may not be providedwith a relatively heavy or highcapacity tuse 1:2, for a purpose to beset forth.-

A transformer core member 13, preferably of the laminated type, ismounted intermediate the fuses 10 and 11 and is provided with aplurality of inductively related coils or windings 14: and 15, which areconnected directly across the terminals of the normalrating t'uses 10and 11, respectively. The coils 14 and 15 preferably comprise the samenumber of turns and, in brief, a 1/1 ratio transformer is thusinterposed between the fuses 10 and 11.

However, the transformer device is normally inoperative by reason at thefact that the only voltage impressed upon the windings 1d and 15 is thatcorresponding to the normal voltage drop across the respective fuses 1iand 11. Consequently, the trans lformer device has practically no effectupon the nor nal operation of the fuses, but becomes active only afterthe rupture of either the fuse 10 or the fuse 11, as subsequently setforth in detail. Thus it would be permissible to use a fuse ofsubstantially nor mal rating in each branch 4 and 5.

The'operation or the protective device shown in 'llig. 1 under overloadconditions may be set forth" as follows: Duringnormal operatingconditions practically-no current will flow through'the transforn'iercoils l i and 15, sincethe voltage impressed upon the coil. terminals ismerely the voltage drop from one end oli'the corresponding fuse to theother, which drop is, of course, relatively small. However, upon theoccurrence of an overload current, the one or the other of the lowcap'acity fuses 10 and 11 will be ruptured by reason of the provision ofthe relatively large-capacity fuse 12 or no fuse at all in the branchcondiiictor 6.

Assuming that the fuse 10, for example, first interrupts the currenttraversing the branch conductor l, the practical. short circult of thetransformer winding 14- is thereby removed and the protective devicewill then act as a true transformer. voltage will thereby be induced inthe other transformer coil'15 acting as a secondary winding, to

to traverse the low-capacity fuse 11 in ad cause a relatively heavycurrent dition to Whatever current is already tlovw ing therethrough tothe motor Winding.

in effect, the fuse 11 thus short-circuits the secondary winning 15 Withthe result that the fuse 11 is immediately ruptured. Both transformercoils l4 and 15 are now connected in circuit, but lay reason of theconstruction and transformer operation of the protective device, only asmall currentmostly magnetizing-will flow through the branch conductorsi and 5 and the trans former windings. lt will be understood that thetransformer coils i l and 1.5 will be designed of a capacity sufficientto permit the traversal of the necessary currents with out sustainingany injury.

In this Way two of the phases leading to the motor '3 are almostsimultaneously opened, and the motor thus stopped be fore any injurioussingle-plume operation thereof can occur, inasmuch as the magnetizingcurrent in question will not be sufficient to operate or damage themotor.

it Will he understood that :1 correspond ing operation occurs in casethe fuse ll of the branch conductor 5 is first ruptured. in any eventthe fuse 12, if provided, by reason of the large capacity thereof, willnot he ruptured, since the action just described will cause the fuses l0and 11 to open two of the phases before the current is heavy enough tomelt the fuse 12. It Will he understood that fuse 12 is not essential tothe protective operation, since in any event,tvro phases are opened.

Referring to Figure 2, the system here shown comprises thesupply-circuit conductors l, 2 and 3 and the branch or customers circuitconductors i, 5 and 6 for supplying energy to the induction motor 7 orthe like. The fuses l0 and ll are inserted in the branch conductors 4L-and 5 as previously set forth, While a fuse 22 of similar capacity isintroduced in the remaining branch conductor G. The three phase circuitsare thus protected by fuses of equal capacity.

A threedegged transformer core 23, Which may be assembled in atriangular or any other suitable form, is provided with a plurality ofcoils 24,25 and 26 that are Wound upon the respective legs of the coreand are connected across the terminals of the fuses 10, 11 and 22respectively. In this Way, the three fuses may be inductively andoperatively interlinked Whenever any one fuse ruptures.

The operation of this form of my invention will be evident from thepreviously described operation of the system that is shown in Fig. 1.lln the event of an overload rupturing any one of the fuses 10, 11 and22, the corresponding transformer coil, 24 for example, if the fuse 10is ruptured, has sufficient potential impressed across its terminals toinduce voltages of material incomes value in the associated transformercoils and 26, whereby a certain current is caused to traverse each ofthe'fuscs l1 and 22, supplementary to Whatever current is alreadyflowing therethrough, temporarily, to the motor windings. Consequently,the one or the other of the fuses 11 and 22 will be immediat ly rupturedto prevent the duration of single-phase operation of the motor 7.

have thus provided a relatively simple and inexpensive protective devicefor ahsolutely preventing the single-phase operation of a polyphasetranslating device, such as an induction motor. lvly protectiveapparatus may be readily installed in a new equipment or applied to anequipment al ready in use. 'lhere are no moving parts to he maintainedor adjusted and, after the ope 'ation of the proteoivc device, the onlyrenewals necessary are two of the ordinarycapacity fuses. Moreover, suchrenewals do not require any special type of fuse or any special rewiringor other adjustments. In other Words, after the fuses have blown, it ismerely necessary to reinsert similar fuses in the holding clips, theremainder of the protective apparatus requiring no at tentionwhatsoever.

I do not wish to he restricted to the specific circuit connections,structural details or arrangement of parts herein set forth, variousmodifications thereof may he effected without departing from the spiritand scope of my invention. I desire, therefore, that only suchlimitations shall be imposed as are indicated in the appended claims.

claim as my invention:

Llrotective means for a polyphase translating device comprisinginterrupting means in each phase circuit, and a transformer renderedactive upon the operation of one interrupting means for effecting theoperation of another.

2. Protective means for a polyphase translating device comprising fusesin a plurality of phase circuits, and inductive means for materiallyincreasing the current traversing one of said fuses upon a predeterminedincrease in the current traversing another.

8. Protective means for a polyphase translating device comprising fusesin a plurality of phase circuits, and a transformer for increasing thecurrent in one fuse to the rupture point thereof upon a rupture of another fuse.

l. it polyphasecircuit having a relatively high-capacitycircuit-interrupting means in one phase and lower-capacitycircuit-interruptiug means in other phases, and means for efiecting theoperation of one lowercapacity means upon the operation of another.

5. A polyphase circuit having a relatively high-capacity fuse in onephase and lowercapacity fuses in the remaining phases, and

means for inductively efiecting the rupture of one low-capacity fuseupon the rupture of another.

6. A polyphase circuit having a relatively high-capacity fuse in onephase and lowercapacity fuses in two other phases, and a transformerconnected to increase the current in either lower-capacity fuse to therupture point upon the rupture of the other lower-capacity fuse.

7. A polyphase circuit comprising a relatively high-capacity fuse in onephase, lowercapacity fuses in other phases, and a transformer having aplurality of coils connected across the crminals of the respectivelowcapacity fuses.

S. A polyphase circuit comprising a plurality of fuses of differentcapacities, and. means responsive to the rupture of one fuse foreffecting the rupture of another fuse of the same capacity.

9. The combination with a polyphase translating device, of meansresponsive to the interruption of one phase for inductively andoperatively inter-linking all of the phases.

10. A three-phase circuit comprising circuit-interrupting means in eachphase, and a transformer having a plurality of coils respectivelyconnected across said means.

11. A three-phase circuit compri' plurality of similar fuses in thesevere phases and a transformer having a plurality of coils respectivelyconnected across said fuses, whereby upon the rupture of one fuse, saidtransformer becomes effective to increase the current in the other fusesto such a value that the one or the other remaining fuse is ruptured.

12. A three-phase-circuit having protective means in two phase circuitsthereof, and

a single transformer having only two coils, said coils beingrespectively connected to said protective means to effect the operationof both of said means under predetermined current conditions in'saidcircuit.

13. A three-phase circuit having fuses in two phase circuits thereof,and a single transformer having only two coils, said coils beingrespectively connected across said fuses to effect the operation of bothfuses under predetermined current conditions in said circuit.

14. A three-phase circuit having a relatively high-capacity fuse in onephase, lower-capacity fuses in the other two phases, and a transformerhaving only two coils, said coils being respectively connected acrossthe low-capacity fuses to effect the operation of both of said fusesprior to any operation of said hi h-capacity fuse under predeterminedcurrent conditions in said circuit.

15. A polyphase circuit comprising a relatively high-ca pacityprotective means in one phase, lowercapacity protective means in otherphases, a magnetizable core, and a plurality of coils wound on said coreand connected across the terminals of said lowercapacity means only.

16. A polyphase circuit comprising a relatively high-capacity fuse inone phase, lower-capacity fuses in other phases, a continuousmagnetizable core, and a number of coils less than the number of phaseswound on said core and respectively connected across the terminals ofsaid lower-capacity fuses.

In testimony whereof, I have hereunto subscribed my name thistwenty-first day of August, 1922.

WALTER L. HARTZELL.

